Oddly enough I was refreshing my memory about tidal action between solar system bodies a few weeks ago so this is very timely.
After seeing this Cassini news it occurs to me in the case of Enceladus, what we see is a pump, a really-really big pump. How cool is that!
I’ll let the Cassini press release explain:
This set of images from NASA’s Cassini mission shows how the gravitational pull of Saturn affects the amount of spray coming from jets at the active moon Enceladus. Enceladus has the most spray when it is farthest away from Saturn in its orbit (inset image on the left) and the least spray when it is closest to Saturn (inset image on the right).
Water ice and organic particles gush out of fissures known as “tiger stripes” at Enceladus’ south pole. Scientists think the fissures are squeezed shut when the moon is feeling the greatest force of Saturn’s gravity. They theorize the reduction of that gravity allows the fissures to open and release the spray. Enceladus’ orbit is slightly closer to Saturn on one side than the other. A simplified version of that orbit is shown as a white oval.